Here's how to do it:
- Open Winamp Preferences

- select "output plugins" and "Disk Writer" and "configure" it

- In next window choose output directory(folder) where you want your HLSS files to reisde. Mark checkbox "Convert to format". Select "force WAV file" in "Output mode" and mark " Kill null samples" At last press "..." button to choose correct format.
You will be presented a standard Windows sound quality dialog:

Ensure there is a PCM choosen under "format". Select
exactly 8.000 kHz, 16 bit, Mono under "Attributes".
(For your future convenience you can click "Save As..." and enter name of this format, like I named it "Half Life Quality". So next time you won't have to scroll through all those kHz, bits and monos, just choose your saved quality from first combo.)
Now just go OK, OK, OK untill all dialogs close.
Then take all songs you want to convert and put them into Winamp playlist - and press "play". You'll see all songs playing on smth like uberfast-forward and when everythin stops, you can run HLSS and load new sounds.
Don't forget to switch Winamp back to Direct Sound(default) or Wave Out in preferences. Selecting correct plugin as in first image is enough.